The present invention relates to a method of sampling a liquid in a container and more particularly to sampling of a molten salt in a closed container under variable pressure.
U.S. Pat. No. 4,140,594 of Rogers et al. issued Feb. 20, 1979 for "Molten Salt Bath Circulation Patterns in Electrolysis" shows in its FIG. 1 a container for molten salt and is an instance where the present invention can be put to use. Cell containers for chloride electrolysis as disclosed in the 4,140,594 patent are closed to prevent chlorine escape and to keep moisture out. The molten salt bath can have a composition, for example, as follows, in weight percent: NaCl 51.0, LiCl 40.0 AlCl.sub.3 6.5, MgCl.sub.2 2.5, and will be typically at around 715.degree. C., so that aluminum resulting from AlCl.sub.3 electrolysis occurs in molten form. It has been the practice to collect molten salt samples through a tube extending through a port in the lid of such cell down into molten salt above the cell anode. A difficulty encountered is that the pressure in the headspace above the bath can be unexpectedly high, so that, when the valve is opened for running a sample thimble down into the bath to fill the thimble with a sample, the bath can surge up the tube and freeze in the colder parts of the system. When this happens, the sampling system must be partially dismantled and either washed out or else heated to get rid of the solid salt plugs.